Recent years, lithium ion secondary batteries are used for electric accumulators of portable machines such as cell-phones, video camcorders and notebook computers, hybrid cars, and battery cars.
The lithium ion secondary batteries are typically obtained by mixing a mixture, where a substance of a powdery electrode active material (active material) has been mixed with an appropriate amount of a binding agent (binder), with a solvent to prepare a slurry for electrodes, and coating and drying it on a current collector followed by pressure-bonding to thereby form an electrode layer.
As for the binder, a material is used that satisfies solvent resistance to organic solvents used for electrolyte solution of secondary batteries, oxidation or reduction resistance in a drive voltage, etc. Polyvinylidene fluoride (hereinafter abbreviated as “PVDF”) etc. are used as such a material.
On the other hand, nitrogen-containing organic solvents such as amides including N-methyl-2-pyrolidone (hereinafter abbreviated as “NMP”) and ureas are used as a solvent to make the mixture of active materials, binders, etc. into a slurry.
However, there were problems with the nitrogen-containing organic solvents including NMP in that cost for collecting the solvents and environmental load are high, etc. Since NMP has a boiling point as high as 204° C., there was also a problem in that considerable energy is required when drying or collecting and purifying the solvents, for example.
In view of these problems, it has been investigated that a nonionic water-soluble polymer is used as a binder and dissolved or dispersed in water to prepare a slurry for electrodes to thereby produce an electrode.
For example, Patent Document 1 discloses a binding agent that contains carboxymethyl cellulose and a polymer latex. The binding agent containing carboxymethyl cellulose and a polymer latex is excellent in dispersion stability and coating ability, and thus electrode layers with good adhesiveness to current collectors can be obtained.
However, since carboxymethyl cellulose is derived from a natural product, there were problems in that quality thereof is less likely to be consistent between lots supplied, storage stability is poor, etc.
Alternatively, a polymer having an N-vinylacetamide unit has been reported as a water-soluble binder of non-natural derived product.
For example, Patent Document 2 discloses a positive electrode paste for nonaqueous batteries that contains poly(N-vinylacetamide) as a polymer containing a repeating structural unit with an amide structure. The poly(N-vinylacetamide) can allegedly improve required performance of secondary batteries (nonaqueous secondary batteries in particular) such as paste stability, binding ability and electrochemical stability.
Furthermore, Patent Document 3 discloses a resin component that contains as a binder poly(N-vinylacetamide) and a copolymer between ethylene oxide (EO) and propylene oxide (PO). The binder can allegedly provide excellent binding ability and battery properties under environment from low temperature to room temperature.    [Patent Document 1] Japanese Unexamined Patent Application, Publication No. H11-67213    [Patent Document 2] Japanese Unexamined Patent Application, Publication No. 2002-251999    [Patent Document 3] Japanese Unexamined Patent Application, Publication No. 2002-117860